The global drive to reduce NOx and CO2 emissions from diesel engine exhausts has led to the implementation of selective catalytic reduction systems in diesel engine vehicles to reduce the automotive emissions. Selective catalytic reduction systems operate by adding a gaseous or liquid reductant to the exhaust gas stream from an engine. The gaseous or liquid reductant is absorbed onto a catalyst where the reductant reacts with nitrogen oxides in the exhaust gas to form water vapor and nitrogen.
This treatment requires the reducing agent to be administered at a precise concentration and with high quality. The solution must be accurately metered and injected into the exhaust gas stream, where it is hydrolyzed before converting the nitrogen oxide (NOx) to nitrogen (N2) and water (H2O).
As the tailpipe NOx emission standard becomes increasingly stringent, it is desired to diagnose the injection faults to assist with the SCR DeNOx functionality and performance. For example, a stuck injector may cause under-dosing of urea and thus reduced DeNOx functionality.
In order to properly interact with on-board diagnostic systems, such as OBD or OBDII, existing selective catalytic reduction systems include self-diagnostics to identify faults and enable pin point replacement while the vehicle is being serviced. For example, pressure changes may be monitored after commanding the pump to run or shut down. One drawback of this method, however, is that the emissions control process is disrupted. Accordingly, new systems and methods of detecting the SCR closing time are desired.
In addition, determining closing time of injectors for direct fuel injection is also desired, in order to provide for better control and improved fuel economy.